Heat exchange in printed circuit boards is enabled by the thermal interface material (TIM) between the heat source (silicon die) and the heat sink (copper cold plate). While solder-based TIMs have high thermal conductivity, they can melt during reflow procedures, leading to reliability problems. Polymer TIMs are pliant and stay in place through reflow procedures; however, their thermal conductivity is substantially lower than solder TIMs.
This disclosure describes techniques to apply solder and polymer TIMs in a composite manner that leverages their complementary properties - the high thermal conductivity of the solder TIM and the higher reliability of the polymer TIM. Solder TIMs applied in small, non-contiguous tiles are bounded by thin lines of polymer TIMs. Solder-TIM tiles are held in place by the polymer TIMs, thus increasing reliability. Heat exchange, being mostly done by the high-conductivity solder TIM, is efficient.
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n/a, "Thermal Interface Material of High Conductivity and Thermomechanical Reliability", Technical Disclosure Commons, (July 25, 2022)